1. Field of Invention
This invention relates to optical periscopes with integrated video display capabilities.
2. Prior Art
Optical periscopes as described in U.S. Pat. No. 2,361,050 have been in use on ground combat vehicles such as tanks and infantry vehicles for many years. These periscopes are generally wide field of view devices composed mainly of solid glass or acrylic prisms with mirrored surfaces. A cross-section of a conventional periscope is shown in FIG. 1. The armor of the vehicle is represented by 170. Periscopes can be designed to be inserted from outside or inside the vehicle. The variety shown is inserted from the inside. The periscope is enclosed in a metal housing 130. A suitable elastic material such as a two-part Room Temperature Vulcanized (RTV) rubber 190 is used to secure and cushion the optics within the housing. Periscopes generally have an upper prism 110 and a lower prism 120 with reflective coatings on angled surfaces 115 and 125 respectively. The prisms are generally separated by gap 135 containing air, an inert gas, or a vacuum (U.S. Pat. No. 4,149,778), or a transparent elastic solid (U.S. Pat. No. 4,065,206). The purpose of the gap is to isolate the lower prism 120 from the shock of a ballistic impact on the upper portion of the periscope. Frequently there is a laser filter 140, which can be placed as shown at the entrance face, in the air gap, or at the exit face. The function of the filter is to protect the crewmember's eyes from laser damage while using the periscope. A protective faceplate 150, commonly composed of polycarbonate or other transparent shatter-resistant material, is often placed at the exit face of the periscope to prevent pieces of shattered glass or acrylic from entering the crew compartment in the event of a ballistic impact on the periscope. Light 180 from outside of the vehicle enters the periscope at the entrance face, reflects off reflective coating 115, reflects off reflective coating 125, exits the periscope at the exit face, and is visible by the eye of the crewmember 160. Conventional periscopes are used by crewmembers to drive, acquire targets, maintain situational awareness, and perform similar tasks while staying within the protection of the vehicle's armor. Such periscopes often include a blind as described in U.S. Pat. No. 4,033,677 which blocks light inside the vehicle from exiting through the periscope where it could be detected by opposing forces.
The skills involved in operating a ground combat vehicle have historically been trained in a simulator or by live exercises. Over the last decade, significant research has been performed to develop the capability to perform virtual training using the actual vehicle but not requiring movement of the vehicle or firing of actual weapons. This capability is referred to as Embedded Training. For example, embedded gunnery training has been demonstrated in the Abrams Main Battle Tank and Bradley Infantry Fighting Vehicle wherein synthetic imagery was electronically injected into the Forward Looking Infrared (FLIR) sights and the vehicle's controls were used by the crewmembers to engage the simulated targets. Noteworthy as these demonstrations were they underscored the limitations to current approaches to embedded training. Two major shortcomings were the inability to use the periscopes and other optical sights in the training and the inability to perform degraded mode training. The present invention addresses the optical sight shortcoming by integrating a display capability into the periscope.
In addition to enhancing embedded training capabilities a periscope with display capability can also be used as a general purpose display for displaying vehicle data or imagery from sensors or cameras during combat operations or vehicle maintenance functions.
The invention of U.S. Pat. No. 4,672,435 describes an array of displays placed in a circular pattern around the observer for displaying the imagery from a camera mounted in the proper azimuth position on a rotating platform. This method of displaying imagery has the intrinsic problem of introducing displays into an already space constrained vehicle compartment.
The invention of U.S. Pat. No. 5,982,536 improves upon the concept of U.S. Pat. No. 4,672,435 by integrating the display with the periscopes. However, the integration is by static combiner elements which inevitably involve compromises in performance. Specifically, a large portion of the outside light is lost when the device is used to provide an optical view of the outside world and a large portion of the display light is wasted when the device is used to provide a display image.
U.S. Pat. No. 6,844,980 describes an invention in which an electronically controllable image combiner is used to superimpose a display image in the user's line of sight when the combiner is in one electrical state and allow the user to see through the combiner when in another electrical state. However, this invention is defined as a thin substrate positioned generally normal to the direction of the user's line of sight, rather than being integrated into a periscope. Though this approach is an improvement over the static combiner method, it has inherent issues in that power must be continually applied when the image combiner capability is utilized and when power is removed, intentionally or through power failure, the combiner will cause the view to be degraded.
The invention of U.S. Pat. No. 7,056,119 is designed to provide an electronically controllable combination of images within a periscope through the use of electronic shutters and presumably static image combiners. As with the other inventions it too has intrinsic shortcomings, two of which are significant. First, the Polymer Dispersed Liquid Crystal (PDLC) technology used in the invention requires power to make it transparent, which is required when the outside view is desired. This implies that the device must be continuously powered in order for the crewmember to use the periscope in normal operation mode and that the loss of power will make the periscope unusable. The second failing is that the invention relies on Total Internal Reflection (TIR) and the elimination thereof by electronic means. Unfortunately the angles of incidence required to produce TIR do not permit the large field of view generally required of ground vehicle periscopes.
3. Objects and Advantages
Several objects and advantages of the present invention are:
    a) provides for switching between outside view, display view, and a combination of the two within a periscope;    b) display view can be used to show a simulated scene for training purposes;    c) display view can be used to show vehicle data;    d) display view can be used to show video, e.g., from a daylight camera or FLIR;    e) combined view can be used to simultaneously show vehicle data and the outside view;    f) combined view can be used to simultaneously show symbology that is spatially correlated with the outside view (e.g., a target cue) and the outside view itself;    g) combined view can be used to simultaneously show sensor imagery (e.g., from a FLIR) in, for example, low light, obscuring weather, or obscuring smoke viewing conditions;    h) makes efficient use of space;    i) wastes very little of the outside or display light;    j) contains no moving parts which could wear out or jam;    k) failure modes return the device to the optical view of the outside;    l) design can be easily adapted to different size periscopes;    m) provides wide viewing angles;    n) can be permanently installed and used for both training and normal operations;    o) provides optional dimming of outside view;